There are two more options for rewiring these lampholders for parallel ballasts.
Replace all of the non-shunted lampholders with shunted. Wire the new ballast as parallel connecting the new ballast wires directly to the new shunted lampholders (option 2).
Remove all of the existing non-shunted lampholders from the fixture and remove all of the wires from each of these lampholders (option 3). Reinstall lampholders after they are rewired.
3 Lamp Series-Parallel Ballast
After 3 Lamp Ballast is Replaced Option 2
Non-shunted lampholders are replaced with shunted lampholders. Ballast wires are connected directly to the new shunted lampholders.
Wires are removed from existing non-shunted lampholders. Ballast wires are connected directly to one side of the non-shunted lampholders. Each side of the existing lampholders are connected together with a wire to simulate a shunted lampholder.